1. Field of the Invention
The present invention relates to a high-speed, multi-nozzle inkjet apparatus.
2. Description of Related Art
A multi-nozzle inkjet apparatus including a large number of nozzles can print on a medium such as a substrate at a high-speed and at a high density. A multi-nozzle inkjet apparatus including an inkiest head for an on-demand method is disclosed in Japanese Patent Application No.2002-273890. This apparatus has a large number of nozzles and ejects ink particles from the opening of each nozzle by applying pressure to an ink chamber by driving a piezoelectric element or the like. Since an inkjet head for the on-demand method has a simpler structure, several hundred or several thousand nozzles can be disposed at a high density.
Recently, the multi-nozzle inkjet apparatus is used to form thin films. In order to form a thin film by using a multi-nozzle inkjet device, tiny ink droplets on the order of 10 to 20 mg must be ejected uniformly, and variations in the weight of the ink droplets that are ejected from each nozzle must be kept to within a few percent. However, Japanese Patent Application No. 2002-273890 has large variations in the weight of ink droplets ejected from the nozzles, since the nozzles have different nozzle characteristics. In view of commercial profitability, it is difficult to increase the precision of nozzle fabrication and restrain weight variations to within a few percent.
Adjustment of ejection weight is used to suppress weight variations. The adjustment of ejection weight adjusts the ink ejection quantity by finely adjusting each drive voltage waveform that is applied to the piezoelectric element of each nozzle, and thus corrects the ejection weights. Japanese Patent-Application No. 9-11457 discloses an inkjet apparatus performing an adjustment of ejection weight, where the inkjet apparatus is provided with a plurality of drive waveform generators that generate the different drive voltage waveforms respectively, and applies a desired drive voltage waveform to each nozzle.
Japanese Patent-application No. 4-316851 discloses an inkjet apparatus that is provided with a single drive waveform generator that can generate a plurality of drive voltage waveforms, for all the nozzles in common. Since the inkjet apparatus cannot apply different drive voltage waveforms for the nozzles simultaneously, the desired drive voltage waveform is applied to one nozzle at a time sequentially by a time-division method.
Japanese Patent Application No.9-11457 encounters no problem when the number of nozzles is small. However, when there are several hundred or several thousand nozzles, it is difficult to produce the inkjet apparatus since the number of drive waveform generators increases and the circuit for selecting these drive waveform generators becomes more complicated.
Japanese Patent Application No. 4-316851 also encounters no problem when the number of nozzles is small. However, when there are several hundred or several thousand nozzles, the number of time divisions grows too large and thus the number of ejections also increases correspondingly, so the coating speed deteriorates dramatically.